Soft drinks are typically formulated from a combination of carbonated water (soda) and a flavoring syrup. In soft drink beverage dispensing systems, the syrup is preferably dispensed under pressure for a fixed period of time, such period equating to a desired volume of syrup. However, it is well known that syrup viscosity changes with temperature, atomsphere, and various other parameters. Accordingly, if the syrup is dispensed for a fixed period of time at a fixed temperature, the amount of syrup dispensed will be a function of its viscosity, resulting in a "weak" or "strong" drink. In such situations, not at all uncommon in prior systems, the customer or consumer is often dissatisfied with the taste of the drink.
Attempts to compensate for syrup viscosity changes have been extensive and somewhat sophisticated. It has previously been known to monitor the temperature of the syrup and then adjust the timing of the dispensing cycle to compensate for corresponding changes in viscosity. In presently known beverage dispensers, a microprocessor is typically used as the control mechanism for the system. Such a microprocessor readily provides means for achieving such compensation, by simply storing a table which relates temperature to viscosity and, in turn, to flow rates such that the period of the dispensing cycle can be varied to assure the appropriate volume of syrup is dispensed. Typically, the prior art would set its standard dispensing cycle for the thickest anticipated syrup and then shorten the cycle to compensate for the thinner syrups actually experienced. It further has been known to set the standard dispensing cycle in a middle range and then lengthen or shorten the dispensing cycle dependent upon the monitored temperature.
In the prior art, the monitoring of the syrup temperature, while reasonable in theory, has a number of shortcomings. As mentioned above, temperature is only one parameter that affects viscosity, there being several others. By measuring only temperature, there is still no assurance that flow rates and, accordingly, total volume dispensed can actually be controlled. Further, the measurement of the temperature of syrup at one or two points in a system is not necessarily indicative of the temperature throughout the system. Large systems, serving plural dispensing stations from a single supply source, may have syrups displaying different viscosities at different points throughout the system. Finally, the prior art does not really monitor or control the critical parameter of rate of syrup flow, but seeks to extrapolate the affect that temperature will have on flow rate by (1) assuming that flow rate is determined principally by temperature, and (2) assuming that the temperature at one or two points within the system is indicative of the viscosity of the syrup throughout the system.
There is a need in the art for a syrup dispensing system which is responsive to flow rates, not temperature or viscosity, for it is the flow rate of the syrup which is ultimately of paramount importance.